Dashboard spacers out of control?

Node-Red 2.0.6, Dashboard 3.0.4, Firefox

I intended to rearrange the layout of this dashboard, so I started by deleting lots of "spacer 7x1" entries in the right hand column "Layout".

After deploying, there seemed to be even more of them.

I deleted some more and now there lots, lots more of them and they even overlay the bits of the dashboard with real widgets on (part of page screenshot, unwanted spaces with yellow arrow overlaid).

I am afraid to deploy again! How to get rid of them all so I can start again to arrange the layout?

I don't know why they were proliferating but I got rid of them by ensuring all spacers were below all widgets then deleting all the spacers (about a hundred of them by then!)